/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase.procedure2;

import java.util.Iterator;
import java.util.List;
import java.util.concurrent.TimeUnit;

import org.apache.yetus.audience.InterfaceAudience;

import org.apache.hbase.thirdparty.com.google.common.annotations.VisibleForTesting;

/**
 * Keep track of the runnable procedures
 */
@InterfaceAudience.Private
public interface ProcedureScheduler {
    /**
     * Start the scheduler
     */
    void start();

    /**
     * Stop the scheduler
     */
    void stop();

    /**
     * In case the class is blocking on poll() waiting for items to be added,
     * this method should awake poll() and poll() should return.
     */
    void signalAll();

    /**
     * Inserts the specified element at the front of this queue.
     * @param proc the Procedure to add
     */
    void addFront(Procedure proc);

    /**
     * Inserts the specified element at the front of this queue.
     * @param proc the Procedure to add
     * @param notify whether need to notify worker
     */
    void addFront(Procedure proc, boolean notify);

    /**
     * Inserts all elements in the iterator at the front of this queue.
     */
    void addFront(Iterator<Procedure> procedureIterator);

    /**
     * Inserts the specified element at the end of this queue.
     * @param proc the Procedure to add
     */
    void addBack(Procedure proc);

    /**
     * Inserts the specified element at the end of this queue.
     * @param proc the Procedure to add
     * @param notify whether need to notify worker
     */
    void addBack(Procedure proc, boolean notify);

    /**
     * The procedure can't run at the moment.
     * add it back to the queue, giving priority to someone else.
     * @param proc the Procedure to add back to the list
     */
    void yield(Procedure proc);

    /**
     * The procedure in execution completed.
     * This can be implemented to perform cleanups.
     * @param proc the Procedure that completed the execution.
     */
    void completionCleanup(Procedure proc);

    /**
     * @return true if there are procedures available to process, otherwise false.
     */
    boolean hasRunnables();

    /**
     * Fetch one Procedure from the queue
     * @return the Procedure to execute, or null if nothing present.
     */
    Procedure poll();

    /**
     * Fetch one Procedure from the queue
     * @param timeout how long to wait before giving up, in units of unit
     * @param unit a TimeUnit determining how to interpret the timeout parameter
     * @return the Procedure to execute, or null if nothing present.
     */
    Procedure poll(long timeout, TimeUnit unit);

    /**
     * List lock queues.
     * @return the locks
     */
    List<LockedResource> getLocks();

    /**
     * @return {@link LockedResource} for resource of specified type & name. null if resource is not
     *         locked.
     */
    LockedResource getLockResource(LockedResourceType resourceType, String resourceName);

    /**
     * Returns the number of elements in this queue.
     * @return the number of elements in this queue.
     */
    @VisibleForTesting
    int size();

    /**
     * Clear current state of scheduler such that it is equivalent to newly created scheduler.
     * Used for testing failure and recovery. To emulate server crash/restart,
     * {@link ProcedureExecutor} resets its own state and calls clear() on scheduler.
     */
    @VisibleForTesting
    void clear();
}
